Piston assembly for dual-network disk-brake system

ABSTRACT

A vehicle-brake system having a tandem or twin master cylinder for delivering the brake fluid to independent transmission networks each connected with one compartment of a disk brake whose actuating cylinder is located on one side of the brake disk and receives at least one piston defining its working compartments or chambers therein. A pair of pistons are provided, so that the chambers are disposed to one side of the directacting piston while the other piston applies pressure to the brake housing or to a force-transmission frame extending around the disk.

United States Patent 11 1 Marschall et a1. 1451 Aug. 7, 1973 PISTON ASSEMBLY FOR DUAL-NETWORK [52] US. Cl. 188/345, 60154.6 M, 92/75, DISK-BRAKE SYSTEM 188/725 [51] Int. Cl B60t 11/20 [75] wgf gf yigfizxi iggf 58 Field of Search 188/106 P, 345, 72.5;

9 Frankfurt/Fechenheim; Hans Albert 60/54'6 92/50 75 Beller, Bad Wilbel; Heinz Hahm Frankfurt/Main; Juan 1mm, [561 References Cited Walldorf/Hessen, all of Germany UNITED STATES PATENTS 3,027,978 4/1962 Peras 188/725 [73] Assgneeggrg fim g g 3,337,009 8/1967 M6161 188/345 2 d F b 18 1972 y FOREIGN PATENTS OR APPLICATIONS 1 e 951,906 3/1964 Great Britain 188/345 [21] Appl. No.: 227,346 1 Primary Examiner-George E. A. Halvosa Related U.S. Application Data Atmmey Karl E Ross [62] Division of Ser. No. 99,407, Dec. 18, 1970, Pat. No. 3,669,226, which is a division of Ser, No. 831,400, June 9, 1969, Pat. No. 3,601,233, which is a division [57] ABSTBACT fS 631,330, 8, 1967, p 3,490,565 A veh1cle-brake system having a tandem or twin master cylinder for delivering the brake fluid to independent [30 Foreign Application p i Data transmission networks each connected with one corn Nov. 16, 1966 Germany T 32523 Dec. 16, 1966 Germany T 32765 Dec. 16, 1966 Germany T 32766 Dec. 16, 1966 Germany T 32768 Dec. 16, 1966 Germany T 32769 Dec. 17, 1966 Germany..... T 32784 Dec. 17, 1966 Germany T 32785 Feb. 7, 1967 Germany T 33161 partment of a disk brake whose actuating cylinder is located on one side of the brake disk and receives at least one piston defining its working compartments or chambers therein. A pair of pistons are provided, so that the chambers are disposed to one side of the direct-acting piston while the other piston applies pressure to the brake housing or to a force-transmission frame extend ing around the disk.

10 Claims, 7 Drawing Figures PATENTEDAUB mu SHEET 1 BF 3 to rear brake #0 rear brake FIGI llllul'l FlG.lb

FlGJa' PAIENTED 75 SHEEI 2 BF 3 FIG. 2

PATENIED 3, 750.857

SHEET 3 [If 3 FIG.3

Zo8b I 305 303 307 306 aoe 308k 32in FlG.3b

CROSS-REFERENCE TO COPENDING APPLICATION This application is a division of copending application Ser. No. 99,407 filed 18 Dec. 1970 (now U.S. Pat. No. 3,669,226) as a division of application Ser. No. 831,400 filed 9 June 1969 now U.S. Pat. No. 3,601,233), a division of application Ser. No. 681,330 filed 8 Nov. 1967, now U.S. Pat. No 3,490,565 issued 20 Jan. 1970.

FIELD OF THE INVENTION Our present invention relates to improvements in dual-network brake systems and, more particularly, to a piston assembly for dual-network brakes and, especially, disk-type brakes.

BACKGROUND OF THE INVENTION The use of so-called dual-network brake systems, because of increased safety, has gained in interest of late and, in fact, is required in many jurisdictions. The term dual-network brake system as used herein is intended to designate a vehicular brake system in which the master cylinder is subdivided into a pair of chambers, each of which may communicate with a respective compartment of a subdivided brake-fluid reservoir, and receives a respective master-cylinder piston oper ated by the brake pedal of the vehicle.

In so-called tandem master cylinders, the master cylinder chambers are disposed one behind the other and the coaxially aligned but axially spaced pistons received in these chambers can be coupled by rods, springs or force-transmitting systems. From each of the master cylinder chambers, a respective fluidtransmission network of tubes or lines runs to the respective sets of wheel-brake cylinders. In general, earlier systems using dual transmission networks have connected the master-cylinder chambers with respective sets of wheel-brake cylinders. Thus, if the vehicle was equipped with front-wheel brakes and rear-wheel brakes, one transmission network communicated with all of the wheel-brake cylinders of the front-wheel brakes while the other communicated with the wheelbrake cylinders of the rear-wheel brakes; in another arrangement, a number of wheel-brake cylinders were provided on each of the wheel brakes for applying respective pads or brakeshoes against the single rotating surface at each wheel brake.

The rotating surface was either the inner face of a drum when drum-type internal-expansion brakes were employed, or a disk whose braking faces lay in planes generally transversely to its axis of rotation. In devices of the latter type, each of the hydraulic-fluid networks communicated with one of the wheel-brake cylinders of each wheel brake so that, in the event of failure in one fluid-transmission system, the other system would remain effective, albeit to a lesser degree, to brake all of the wheels. In general, disk-brake assembles using wheel-brake cylinders mounted in opposite lobes of a support yoke extending around the periphery of the disk have proved to be of relatively complex manufacture, especially since the numerous cylinder bores must be precision-formed independentlyof one another.

OBJECTS OF THE INVENTION It is, therefore, the principal object of the present invention to provide an improved disk-brake system for automotive vehicles which may be operable by dualnetwork master cylinders and the like and yet avoid the disadvantages of prior-art brake systems.

A corollary object of this invention is to provide an improved fluid-responsive cylinder assembly for disktype brakes.

Yet another object of our invention is to provide an improved dual-network brake system for automotive vehicles which is of reduced cost and complexity by comparison with earlier systems.

Yet a further object of the instant invention is to provide a disk brake for automotive vehicles which can be energized from a tandem or twin master cylinder and yet has an actuating cylinder on only one side of the wheel-brake housing.

A more specific object of this invention is to provide a disk brake capable of withstanding the stresses resulting from frictional engagement of the brakeshoes with the disk and yet of relatively small dimensions and with a minimum number of parts and few force-transmitting members.

Another object of our invention is to provide a disk brake in a dual-network brake system in which the failure of one of the networks will not give rise to unduly increased brake-pedal stroke and which applies substantially the same braking frictional surface and/or brake force in spite of such failure.

SUMMARY OF THE INVENTION We have now found that these objects can be achieved in a disk-brake system which comprises a brake housing reaching around the periphery of a brake disk connected with a wheel of the automotive vehicle and having at one side of this disk an actuating cylinder containing at least one piston subdividing this cylinder into a pair of independent working chambers effective to urge the brakeshoes flanking the disk in opposite directions against the latter, the chambers being supplied with brake fluid from respective fluidtran smission networks to which the brake fluid is delivered from dual-compartment master cylinder assemblies. The master-cylinder assemblies can include tandem-type master cylinders in which the compartments are disposed one behind the other, or so-called twin" master cylinders in which the compartments are disposed side by side.

According to a particular feature of this invention, the brake housing is shiftable relatively to the disk and bears directly against the brakeshoe remote from the actuating cylinder so that reaction force generated by supplying fluid under pressure to the aforementioned chambers shifts the brake yoke to indirectly apply its brakeshoes to the disk.

Still another aspect of this invention resides in the mounting of the brake housing carrying the actuating cylinder fixedly with respect to the disk, whereby a force-transmission member defines the second compartment with the direct-acting piston which may also he stepped in the manner indicated. In this case, we have found it desirable to constitute the forcetransmitting member as a frame extending around the disk and the brake housing and shiftable relatively thereto, the frame lying in a plane which intersects the disk along a secant thereof. Thus, either the frame or the brake housing may be the force-transmitting member for applying the remote brakeshoe to the disk. The force-transmitting member can, in accordance with a particular feature of the invention, be mounted so as to constitute a floating or swingable element; alternatively or additionally, a parallelogrammatic linkage may be provided between this movable element and the stationary part of the vehicle body or frame, e.g. the axle housing. Moreover, we have found it to be advantageous to constitute one or both of the pistons as cupshaped members receiving a self-adjusting mechanism for advancing the rest position of the piston to compensate for brake-lining wear and/or to lock the piston together upon failure of the fluid-transmission lines, thereby allowing one of the chambers to operate the brake as fully as if both pistons would be pressurized. In this connection, a disk-shaped piston may be provided which either serves as one of the pistons in a movable-yoke arrangement, or forms a partition between the pistons and acts as a force-transmitting member upon failure in one of the transmission lines.

Advantageously, the actuating cylinder is provided with a minimum number of sealing rings engaging the piston or pistons along their cylindrical peripheries at locations remote from the working chambers defined thereby. Moreover, the passages communicating with the chambers may open axially or radially into the latter and the brake housing or yoke, whether stationary or movable, is of a unitary construction and U-shaped configuration so as to take up the lateral stress upon the brakeshoes. We have further found that it is desirable, whether the housing is shiftable or rigid, to provide a secondary or auxiliary yoke extending around the periphery of the disk and flanking the brake housing to take up at least in part the lateral stresses derived upon engagement of the brakeshoes with the disk.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a diagrammatic view of a vehicle-brake system using a tandem master cylinder;

FIG. 1A is a cross-sectional view showing how the yoke of FIG. 1 is supported laterally;

FIG. 1B is an elevational view showing a parallelogrammatic linkage coupling the brake housing of FIG. 1 with a stationary portion of the vehicle, namely its axle housing;

FIG. 2 is a view similar to FIG. 1 of a system with twin master cylinder;

FIG. 3 is a fragmentary axial cross-sectional view of a disk brake having a force-transmission frame, a stepped piston and a relatively stationary brake hous- "'8;

FIG. 3A is a perspective view diagrammatically illustrating the relationship of the frame to the brake housing; and

FIG. 3B is an axial cross-sectional view of a modification of the system of FIG. 3.

SPECIFIC DESCRIPTION In FIGS. I and 1A, we show a disk-brake system in which the unitary, U-shaped brake yoke 6 is provided with a single-step cylinder 6a at the right-hand lobe of the yoke and reaches around the periphery of the brake disk 1 with a flange 6b to engage a brakeshoe whose lining confronts the braking surface or face of the disk 1. The lining is bounded to a backing plate which is affixed to the downwardly turned flange 6b of the yoke 6.

A frame 12 is provided to flank the yoke 6 (see FIG. 1A) and take up the torque applied to this frame when the yoke 6 seizes the disk 1 at 12'. This auxiliary yoke or frame 12 is secured to the vehicle shaft, body or chassis frame so as to be rigid therewith.

The yoke 6 can, of course, form part of a floating or oscillating (swingable) housing structure of the type conveniently used in diskbrakes in which the yoke is movable to permit the actuating means to be disposed at only one side of the disk. An assembly of this character may also be formed with a parallelogrammatic linkage 13 as illustrated for example in FIG. 1B. Thus, the yoke 6 may be provided with a pair of lugs 6e and 6e" in axially spaced relation in which a pair of parallel links 13a and 13b are pivotally mounted. The links 13a and 13b may also be pivotally connected at their opposite ends to lugs 13c, 13c" coplanar with the lugs 6e and 6e" spaced apart by identical distances.

The lengths of the links 13a and 13b are identical. Consequently, the distance between the axes of lugs 6e and 6e" forms one fixed-length arm of the yoke 6 while the other arm is defined between the lugs 13c and of the axle housing 13d. One or more of the pivots joining the arms 13a and 13b with the lugs may be provided with a friction member preventing displacement of the linkage 13 except under the hydraulic action of the brake.

The yoke 6, however, will move parallel to itself as represented by arrow C. It will be understood that the frame 12 or the linkage 13 may be used for the brake yokes of all subsequently described embodiments whenever a movement of the yoke relative to the disk is required to transfer force to the brakcshoe opposite the side of the yoke in which the actuating cylinder is provided. Moreover, the linkage 13 can be considered representative of both swingable and floating yokes since, while the yoke 6 moves parallel to itself (arrow C), it nevertheless swings about the pivots formed by the lugs 13c and 130" and shifts axially as a floatingyoke housing.

Reverting to FIGS. 1 and 1A, it can be seen that the assembly of FIG. 1 is supplied with brake fluid from a tandem master cylinder 14 which is actuated by a brake pedal 14a to displace brake fluid into the independent fluid-transmission networks 14b and 14c. Further wheel brakes may be energized in parallel. Thus the network 14b communicates with one working chamber behind the piston face 15 while network communicates with the other working compartment of the wheel brake. The tandem cylinder 14 is representative of the two-compartment master cylinders designed to function with each of the wheel-brake arrangements described below. I

In normal operation, depression of the brake pedal 14a drives hydraulic fluid simultaneously to both net works 1412 and 14c, thereby distributing it similarly to the wheel brakes 15, etc. of the vehicle. In FIG. I, the configuration of only one of these wheel brakes is shown, although it will be understood that all of the wheel brakes are similarly constructed.

In FIG. 2, we show another embodiment of this invention wherein the U-shaped yoke 106 extending around the periphery of the disk 101 draws a brakeshoe thereagainst when hydraulic fluid is supplied to the cylinder lobe 106a of the brake, as is described below. Along the other flank of the disk 101, we provide a brakeshoe whose lining engages the disk 101 when urged in the direction A by a piston structureslidable in the cylinder as described hereinafter.

In this embodiment, the master cylinder 114 is of the twin-cylinder type which in the cylinder chambers are disposed side by side for joint operation by the brake pedal 114a. All of the wheel brakes may be of the construction illustrated in section in FIG. 2 and may be operated in parallel. The yoke 106 may be mounted in the frame illustrated at 12 in FIG. 1A and may be a floating or swingable yoke, as previously described, and can be provided with the parallelogrammatic linkage 13 in FIG. 18. It will be understood that FIGS. 1A and 1B correspond to views of the assembly in FIG. 2 provided with these variants. Moreover, the twin cylinder 114 will be understood as suitable for use with the wheel brakes of any of the preceding and succeeding Figures.

In FIGS. 3, 3A and 38, we show an embodiment of a system suitable for use with that of FIG. 1 or FIG. 2 wherein a unitary stepped piston on one side of the brake housing is slidably received in a pair of working chambers supplied from individual compartments of the master cylinder. In the system of FIG. 2, by contract, the stepped bore is provided in the axially shiftable housing which, as has been indicated, is a floating, swingable or similar yoke (e.g. connected via the parallelogrammatic linkage 13 with the vehicle frame). In the system of FIGS. 3, 3A and 3B, asimplified forcetransmission structure is illustrated.

Referring initially to FIG. 3, it can be seen that the basic components of this modification consist of a generally U-shaped yoke 206 whose bifurcate arms 206' and 206" reach around the periphery of the disk 201 which, as has been previously indicated, is coupled with the rotatable portion of the vehicle-wheel assembly, e.g. the tire-carrying disk and axle. The yoke or housing 206 is affixed at the right-hand side to the axle housing or vehicle frame by a flange 216 whose bores 216a receive bolts for attaching it to the axle housing as is conveniently done with fixed-yoke disk brakes. Between the arms 206' and 206" of the yoke, which serves to retain the brakeshoes 202, 204 and 203, 205, an opening 206b may be provided to permit inspection of the brakeshoes and to facilitate access thereto.

The cylinder 206a of the yoke is formed with a single-diameter bore 206 in which the stepped piston 207, 208 is axially shiftable. The larger-diameter step 207 bears directly upon the backing plate 205 whose brakeshoe lining 203 confronts the right-hand side of the brake disk 201 and defines within the bore 206a a large-diameter working chamber 218 to which fluid is supplied through a radial bore 206d from one of the compartments of a dual-network master cylinder, e.g. the twin master cylinder of FIG. 2 or the tandem master cylinder of FIG. 1 via the respective brake-fluid networks 1412, 140 or 114b, 114a.

An essential feature of this aspect of the invention is the provision of aninwardly open hollow piston 219 which is axially telescoped with the small-diameter step 208 and defines the small-diameter chamber 219a therewith. The working face 208a of member 219 is effective, upon the delivery of brake fluid to the chamber 219a to urge the brakeshoe 202, 204 to the right.

piston. A single annular seal 210 recessed in the wall of bore 206a engages the large-diameter step 207 at a location remote from its chamber 218, while a further seal 21] recessed in the interior of piston 219 engages the small diameter step 208 at a location remote from chamber 2190. The additional seals 220 and 220 prevent leakage between the piston 219 and the housing 206. A pair of cuffs 209' bridge the cylinder 206a and the backing plate 205 and piston 1219, respectively, to prevent entry of contaminants into the cylinder bore.

The force-transmission means of this modification comprises a frame 221 (see FIG. 3A) which lies in a plane parallel to the axis of the cylinder bore 206a and perpendicular to the braking faces of the disk, generally along a secant of the disk. This frame 221 has inward projections 221a and 221b bearing upon the backing plate 204 of the left-hand brakeshoe whose lining 202 confronts the disk 20], and! upon the outer surface of the piston 219. Thus, when the piston 219 is urged in the direction of arrow B, the frame 221 transfers corresponding movement to the brakeshoe 202, 204 and draws the latter against the left-hand side of the disk. To prevent rotation of the piston 219 and the frame relatively to the fixed housing206, the frame 221 may be guided between lugs 222 extending laterally from the housing 206 (see FIG. 3A).

When neither fluid-transmission network is defective, fluid under pressure is delivered simultaneously to the chambers 218 and 219a, thereby urging the piston 207, 208 to the left (arrow A), while the reaction force is applied to piston 219 to drive the brakeshoe 202, 204 to the right (arrow B). If one of the brake-fluid networks fails, for instance the network supplying chamber 219a, fluid will be delivered in the usual manner to the outer annular compartment2l8 and thereby urge the large-diameter step 207 in the direction of arrow A, and the piston 219 in the direction of arrow B, as previously described. Conversely, failure of the network supplying chamber 218 will nevertheless permit fluid to be delivered to chamber 2190, thereby urging the small-diameter step 208' in the direction of arrow A, and the piston 219 in the direction of arrow B. In either case, the stroke of the brake pedal necessary for actuatingthe brake remains constant in the event of failure of one of the transmission networks, although the amount of foot pressure required for the same braking effect is double. Here again, failure of one of the transmission networks does not decrease the frictional area of the brake which is affected.

FIG. 3B shows a modification of the system of FIG. 3, although the view of FIG. 3A pertains as well to this Figure. The brake fluid from line 3140 is here delivered through the frame 321, and the projection 321a to an axial bore 3081; in the piston 319 which is axially shiftable in the cylinder bore 306a of housing 306. The in- V termediate seal 220 is eliminated and only a single seal 320' need engage the outer periphery of piston 319 at a location remote from the chamber 318. Fluid is delivered to this chamber by a radial bore 306d in the housing 306, as previously described. The stepped piston 307, 308, the piston 319 and the brakeshoes 303, 305 and 302, 304 cooperate with the disk 301, as described in connection with FIGS. 3 and 3A. In both of these systems, the circumferential entrainment of the brakeshoes is blocked by the fixed yoke 206, 306. Furthermore, the yoke 206 may be flanked by the auxiliary yoke structure shown at 12 in FIG. 1A.

We claim: 1. A vehicle-brake system comprising: dual-compartment master-cylinder means foe independently displacing at least two brake-fluid streams;

a pair of transmission networks each connected to' one of said compartments for transmission of the brake fluid dis-placed from said compartments;

and at least one disk brake including:

a rotatable brake disk;

a nonrotatable housing reaching around the periphery of the disk and forming on only one side thereof an actuating cylinder;

a pair of breakshoes flanking said disk including a first breakshoe remote from said cylinder and in force-transmitting relationship therewith and a second brakeshoe proximal to said cylinder;

piston means in said cylinder acting upon said brake shoes and subdividing said cylinder into a pair of independent working chambers respectively communicating with said networks, said piston means including a first stepped piston acting upon said second brakeshoe proximal thereto, said stepped piston having a large-diameter portion defining in part an outer annular one of said chambers and a small diameter portion defining an inner one of said chambers coaxial with the outer chamber,

a second piston having a diameter corresponding essentially to the large-diameter portion of the first-mentioned piston and telescopingly receiving said small-diameter portion thereof while defining within said second piston said inner chamber; and

force-transmitting means connecting said second piston with said first brakeshoe.

2. The system defined in claim 1 wherein said cylinder is axially open at its ends and said pistons are of substantially similar configuration and disposed mirror-symmetrically in said cylinder.

3. The system defined in claim 1 wherein said second piston is formed with a radial bore communicating with said inner chamber, said cylinder having a recess extending in the direction of displacement of said second piston and registering with said bore, and a radial passage formed in said cylinder communicating with said recess for delivering brake fluid to said inner chamber in all positions of said second piston.

4. The system defined in claim 1 wherein said second piston is formed with an axially extending passage communicating between the respective transmission network and said inner chamber.

5. The system defined in claim 1 wherein a pair of relatively slidable annular surfaces form part of said pistons and the means defining said chambers in said cylinder, said disk brake further comprising a pair of annular seals respectively engaging said surfaces at locations remote from the respective chambers.

6. The system defined in claim 1 wherein said housing is a floating yoke.

7. The system defined in claim 1 wherein said housing is a swingable yoke.

8. The system defined in claim 1, further comprising a parallelogrammatic linkage connected to said housing for movably supporting same relatively to said disk.

9. The system defined in claim I wherein said force transmission means comprise a frame extending around said disk and said housing and engaging said first brake shoe.

10. The system defined in claim 9 wherein said frame lies in a plane intersecting said disk along a second and said housing is fixed relatively to said disk, said housing being of U-shaped configuration and unitary construction while forming lateral stops for said brakeshoes upon their frictional engagement with said disk. 

1. A vehicle-brake system comprising: dual-compartment master-cylinder means for independently displacing at least two brake-fluid streams; a pair of transmission networks each connected to one of said compartments for transmission of the brake fluid displaced from said compartments; and at least one disk brake including: a rotatable brake disk; a nonrotatable housing reaching around the periphery of the disk and forming on only one side thereof an actuating cylinder; a pair of breakshoes flanking said disk including a first brakeshoe remote from said cylinder and in force-transmitting relationship therewith and a second brakeshoe proximal to said cylinder; piston means in said cylinder acting upon said brake shoes and subdividing said cylinder into a pair of independent working chambers respectively communicating with said networks, said piston means including a first stepped piston acting upon said second brakeshoe proximal thereto, said stepped piston having a large-diameter portion defining in part an outer annular one of said chambers and a small diameter portion defining an inner one of said chambers coaxial with the outer chamber, a second piston having a diameter corresponding essentially to the large-diameter portion of the fiRst-mentioned piston and telescopingly receiving said small-diameter portion thereof while defining within said second piston said inner chamber; and force-transmitting means connecting said second piston with said first brakeshoe.
 2. The system defined in claim 1 wherein said cylinder is axially open at its ends and said pistons are of substantially similar configuration and disposed mirror-symmetrically in said cylinder.
 3. The system defined in claim 1 wherein said second piston is formed with a radial bore communicating with said inner chamber, said cylinder having a recess extending in the direction of displacement of said second piston and registering with said bore, and a radial passage formed in said cylinder communicating with said recess for delivering brake fluid to said inner chamber in all positions of said second piston.
 4. The system defined in claim 1 wherein said second piston is formed with an axially extending passage communicating between the respective transmission network and said inner chamber.
 5. The system defined in claim 1 wherein a pair of relatively slidable annular surfaces form part of said pistons and the means defining said chambers in said cylinder, said disk brake further comprising a pair of annular seals respectively engaging said surfaces at locations remote from the respective chambers.
 6. The system defined in claim 1 wherein said housing is a floating yoke.
 7. The system defined in claim 1 wherein said housing is a swingable yoke.
 8. The system defined in claim 1, further comprising a parallelogrammatic linkage connected to said housing for movably supporting same relatively to said disk.
 9. The system defined in claim 1 wherein said force transmission means comprise a frame extending around said disk and said housing and engaging said first brakeshoe.
 10. The system defined in claim 9 wherein said frame lies in a plane intersecting said disk along a secand and said housing is fixed relatively to said disk, said housing being of U-shaped configuration and unitary construction while forming lateral stops for said brakeshoes upon their frictional engagement with said disk. 